44 WEEVIL-RESISTING ADAPTATIONS OP COTTON. 



drying of the square does not necessarily destroy the larva, and that a square 

 may undergo far more exposure to direct sunshine than had been supposed 

 possible without causing the death of the larva or pupa within." a » 



It is to be remembered, however, that such disconnected squares are 

 thoroughly dampened every night by the dew. and that a small 

 amount of moisture may pass out from the plant through the shred 

 of dead tissue. In either case the hanging boll might get more moist- 

 ure and less heat than if lying on the dry ground, exposed to full 

 sunlight. Suspended bolls are exposed to air temperatures only. 



If no other means of avoiding the weevil becomes practicable a 

 great extension of the cotton production into the semiaricl districts of 

 western Texas, Oklahoma, and even Kansas is to be expected. The 

 long days of the more northern districts will conduce to the shorten- 

 ing of the growing season, and if dry weather cuts down the yield the 

 loss is likely to be neutralized by more or less complete protection 

 against the weevils. 



These contradictory effects of the same adaptation depending upon 

 climatic condition may render necessary a complete differentiation of 

 the cotton varieties of wet and dry regions. 



It is not improbable that the Upland varieties previously known in 

 the United States came originally from the more or less arid regions 

 of Mexico, where absence or very small development of the basal 

 branches keeps the ground from being constantly shaded and gives 

 better chances for the weevils to be killed by the drying out of the 

 fallen squares. 



Our Upland cottons are undoubtedly of American origin, but the 

 region from which they came has not been ascertained. Some of the 

 Texas varieties are said to have been brought from Mexico. Coro- 

 nado's Journal of the earliest Spanish exploration in Arizona and 

 New Mexico contains many references to the cultivation of cotton by 

 the Indians. There can be little doubt that the agricultural Indians 

 of the Gulf region also cultivated cotton, though no documentary 

 evidence of the fact seems to have come to light as yet. 



It is highly probable that the original home of the cotton plant, and 

 of the boll weevil as well, was in a somewhat arid region, since it is 

 only under such conditions that the weevil would be effectually pre- 

 vented from increasing to the fatal degree of destroying its host 

 plant, and thus cutting off its only means of subsistence. On the 

 other hand, it was only in a humid country like eastern Guatemala 

 that many of these weevil-resisting adaptations would be likely to 

 develop if, as now appears, it has required the selective influence of 

 the boll weevil itself to bring them to their present advanced develop- 

 ment. 



a Hunter. W. D., and Hinds. W. E., 1904. The Mexican Cotton Boll Weevil. 

 Bui. 45, Division of Entomology, U. S. Department of Agriculture, pp. 73 and 74. 



